Work in prokaryotic organisms over the past several years has revealed the presence of discrete genetic elements which are capable of translocation as individual intact units from one position in DNA to another. These same elements have also been found to promote other types of illegitimate recombination events such as the formation of deletions and, in one case, inversions. The objective of the proposed research is to increase our understanding of the molecular mechanism(s) of illegitimate recombination events promoted by or involving one particular translocatable element, the tetracycline resistance element Tn10. The goal of the particular experiments proposed here is to analyze, at the nucleotide sequence level, the particular regions of DNA sequence ("sites") known to be involved in the several different types of TN10-promoted illegitimate recombination events which we have thus far identified: translocation, deletion formation, inversions, precise excision, and "nearly" precise excision. The proposed experiments will probe the nature of the sites involved in these events as well as the relationships among the different types of sites. We hope that the results will give us new insight into the ways in which known DNA sites and segments interact during Tn10-promoted recombination events.